If your blood sugar is high, the most effective immediate steps are drinking water, taking a walk (if your levels are below 270 mg/dL), and, if you use insulin, administering a correction dose. A fasting blood sugar above 130 mg/dL or a reading above 180 mg/dL after meals is generally considered high for people with diabetes. What you do next depends on how high the number is and whether you’re showing other symptoms.
Know Your Numbers First
Normal fasting blood sugar falls below 100 mg/dL. Between 100 and 125 mg/dL is the prediabetes range. A fasting level of 126 mg/dL or higher, confirmed on two separate tests, indicates diabetes. After eating, blood sugar in a healthy person typically stays below 140 mg/dL, while readings above 200 mg/dL at any time suggest a serious problem.
These thresholds matter because your response should match the severity. A reading of 180 mg/dL calls for different action than one above 300 mg/dL. If you’re checking your blood sugar and it’s mildly elevated, you have time to bring it down with simple steps. If it’s very high and you’re feeling sick, that’s a different situation entirely.
Drink Water
When blood sugar is elevated, your kidneys work harder to filter the excess glucose, pulling water from your body in the process. That’s why high blood sugar makes you urinate more often and feel thirsty. Drinking water helps your kidneys flush out some of the extra glucose through urine and prevents dehydration from making things worse. Aim for a full glass right away and continue sipping steadily over the next few hours. Stick to plain water or unsweetened drinks, not juice or soda.
Move Your Body (With One Important Exception)
Physical activity is one of the fastest ways to lower blood sugar without medication. When your muscles contract during exercise, they pull glucose out of your bloodstream for energy, even without insulin’s help. A 15- to 30-minute walk can make a noticeable difference.
There is a critical exception. If your blood sugar is above 270 mg/dL, exercise can actually make things worse. At very high levels, your body may not have enough insulin to let your muscles use that glucose. Instead of lowering blood sugar, exercise forces your body to break down fat for fuel, producing acidic byproducts called ketones. If you have ketones in your system and you exercise, you risk a dangerous condition called ketoacidosis. Check your urine for ketones before working out if your reading is above 270 mg/dL, and wait until ketones are absent before you exercise.
Use a Correction Dose if You Take Insulin
If you’re on insulin, a correction dose is the standard tool for bringing down a high reading. How much insulin you need depends on your individual sensitivity. Your body’s response to insulin is calculated using something called an insulin sensitivity factor: the number of points one unit of insulin will lower your blood sugar. Your doctor or diabetes educator helps you determine this number based on your total daily insulin dose.
For example, if one unit of rapid-acting insulin drops your blood sugar by 50 mg/dL and you’re 150 points above your target, you’d take 3 units as a correction. This math should already be part of your diabetes management plan. If you don’t have a correction factor established, this is worth discussing at your next appointment.
After taking a correction dose, wait about 3 hours before rechecking your blood sugar. Rapid-acting insulin takes time to work fully, and testing too soon can lead you to take additional insulin before the first dose has finished its job. Stacking doses this way is a common cause of dangerous low blood sugar.
Watch What You Eat Next
If your blood sugar is already high, eating more carbohydrates will push it higher. Skip the bread, rice, crackers, and anything sweetened. Instead, reach for foods that won’t add to the spike. Good options include raw vegetables, a handful of nuts, hard-boiled eggs, cheese, or a small portion of fresh fruit paired with protein. The protein and fat slow digestion and prevent the rapid glucose surges that highly processed snacks cause.
As a general guideline, snacks with fewer than 5 grams of carbohydrates have minimal impact on blood sugar. If you need something more substantial, keeping carbs between 15 and 20 grams and pairing them with protein or healthy fat helps maintain steadier levels. Whole foods like vegetables, nuts, and whole grains contain fiber that slows glucose absorption, while processed snacks loaded with refined carbohydrates do the opposite.
Recheck on a Schedule
Don’t just treat a high reading and forget about it. If your blood sugar is 250 mg/dL or above, check it every 4 to 6 hours and test your urine for ketones each time. This monitoring is especially important when you’re sick, since illness and infection commonly drive blood sugar up and can trigger a rapid decline into dangerous territory.
If you took a correction dose of insulin, recheck at the 3-hour mark. If your levels haven’t come down meaningfully, something else may be going on: a missed dose, an insulin pump malfunction, illness, stress, or a medication interaction. Persistent high readings that don’t respond to your usual correction plan warrant a call to your healthcare provider.
When High Blood Sugar Becomes an Emergency
Most high blood sugar episodes are uncomfortable but manageable. Some are life-threatening. Diabetic ketoacidosis (DKA) happens when the body has so little usable insulin that it begins breaking down fat at a dangerous rate, flooding the blood with acids. It develops over hours and can be fatal without treatment.
The early warning signs are intense thirst and urinating far more than usual. As DKA progresses, symptoms escalate: fast, deep breathing; nausea and vomiting; stomach pain; fruity-smelling breath; extreme fatigue; dry skin and mouth; flushed face; headache; and muscle aches. Call 911 or go to the emergency room if any of the following apply:
- Blood sugar stays at 300 mg/dL or above despite correction efforts
- Fruity-smelling breath
- Vomiting with inability to keep food or liquids down
- Difficulty breathing
- Multiple DKA symptoms occurring together
DKA is most common in people with type 1 diabetes, but it can happen with type 2 diabetes as well, particularly during illness or infection. High ketone levels in a urine test are the clearest early warning sign.
Common Reasons Blood Sugar Spikes
Understanding why your blood sugar went high in the first place can help you prevent it from happening again. The most common culprits are eating more carbohydrates than planned, missing or mistiming a medication dose, physical or emotional stress, illness or infection, dehydration, and poor sleep. Some medications, including steroids, can also raise blood sugar significantly.
For people on insulin pumps, a kinked or dislodged infusion set is a frequent and easily overlooked cause of unexplained highs. If your blood sugar is rising for no clear reason and you use a pump, check the tubing and insertion site before assuming you need more insulin.
Occasional spikes happen to everyone managing diabetes. The goal isn’t perfection. It’s having a clear plan so that when a high reading appears on your meter, you know exactly what to do, in what order, and when to escalate.